Fluororesins are used as coatings because they have the characteristics of being chemical resistant, non-tacky, heat resistant, having a low coefficient of friction, and being electrically insulating, as well as because they can form a coating film that is free from pinholes. However, fluororesins cannot be used as a solution for coatings because they are insoluble in water and organic liquids. Therefore, these are applied to an object being coated by means such as, for example, electrostatic painting with a powder coating, or spraying, dipping, or flow coating of a dispersion, such as an organic liquid dispersion or aqueous dispersion stabilized with a surfactant, and then a coating film is formed by heat fusion treatment.
When coating various metallic substrates with fluororesins, such as PTFE, FEP, PFA, or the like, adhesion defects occur and it is very difficult to directly coat the metallic substrate with fluororesin because the non-tacky characteristics of fluororesins make adhesion to the substrate problematic. Therefore, when performing fluororesin coating, primer compositions have been developed and put into use that are adhesive toward the substrate and that are additionally adhesive to fluororesin coatings that will be applied thereover.
However, fluororesin laminates that use the primer compositions have problems in that, when repeatedly challenged by infiltration of heat, moisture, corrosives, or the like, the coating will deteriorate, developing peeling between the top coating layer and primer layer, between an intermediate coating layer and the primer layer, within the primer coating layer, or between the primer layer and the substrate material.
The applicant in this matter has previously proposed a coating composition, in which colloidal particles are contained in a melt processible fluororesin powder dispersion, as a fluororesin coating composition that does not pose an explosion hazard, and that is capable of forming a 100 to 1000 μm-thick coating film having excellent corrosion resistance and steam resistance by a single process of film formation, using a simple paint gun, or the like (Japanese Unexamined Patent Application Publication No. H11-241045 and 2000-80329). However, since this coating composition has a low concentration of colloidal particles in the dispersion used as the coating composition, large quantities of the dispersion must be used to obtain the coating composition using this dispersion of colloidal particles, and the coating composition is difficult to use due to the decreased viscosity of the coating composition. See, for example, Patent Publication: Japanese Unexamined Patent Application Publication No. H11-241045; and Patent Publication: Japanese Unexamined Patent Application Publication No. 2000-80329.
The present invention resolves the aforementioned problems, and an objective thereof is to provide a polymer particle that is non-tacky while at the same time having excellent adhesion to substrate materials and between layers, prevents peeling of the fluororesin laminate by suppressing infiltration of heat, moisture, corrosives, and the like, and that improves corrosion resistance, steam resistance, and durability.
Another object of the present invention is to provide an aqueous dispersion that contains polymer particles with the aforementioned characteristics, and a method of manufacturing the same.
Another object of the present invention is to provide an aqueous fluororesin coating composition that allows a fluororesin laminate to be formed therefrom that is non-tacky while at the same time having excellent adhesion to substrate materials and between layers, prevents peeling by suppressing infiltration of heat, moisture, corrosives, and the like, and that improves corrosion resistance, steam resistance, and durability.